1. Field of the Invention
The present invention relates to inductors and methods for providing inductors in an Integrated Circuit. More particularly, the present invention relates to inductors that permit the implementation of high performance filters and ESD protection in an Integrated Circuit.
2. Description of Related Art
Modern electronic systems, especially mobile wireless applications, require the implementation of circuits having filtering and electrostatic discharge protection attributes. In addition, the systems must consume very little space and therefore demand solutions with extremely small footprints. Since these systems are prevalent in many consumer applications such as cellular handsets it is important that component cost be minimized. In wireless applications such as cellular handsets, filters are required to separate base band information frequencies from radio frequencies (“RF”) carrier signals.
Referring to FIG. 1, a low pass filter is often used to separate base band and RF frequencies. The low pass filter has a certain insertion loss and provides a pass band 180 that has a direct current (“DC”) starting frequency 100 and terminates at the filter cutoff frequency 102. The cutoff frequency 102 is defined as that frequency at which the attenuation is 3 dB greater than the attenuation at DC.
As frequency increases beyond the cutoff frequency 102, the filter exhibits a roll off 12 with increasing attenuation at higher frequencies until a resonant point 14 is reached at which time the response usually reaches maximum attenuation. Beyond this point, the response generally exhibits a return upward (decreasing attenuation) 16.
Now referring also to FIG. 2, in a typical cellular telephone application, it is desirable to have a filter pass band 18 capable of permitting signals containing desired information to pass from one circuit or system block to another while severely attenuating the high frequencies associated with a carrier signal. These RF frequencies are typically in the range from 800 MHz to 2.7 GHz. Low pass filter components can keep RF energy generated outside the phone from entering the phone, prevent RF energy generated within the handset from radiating to the outside environment and limit adverse interactions of the RF and base band sections within the phone. As shown in FIG. 2, an example of potential undesired energy exchange may occur in flexible wiring 20 connecting the base 22 of a flip phone to the top 24 of a flip phone.
Current integrated resistor capacitor (“RC”) implementations of low pass filters have been fabricated and can provide reasonable performance in meeting current requirements. However, as system data rate demands continue to increase, for example in the processing of larger quantities of multimedia information for higher resolution displays, the desire to have low pass filters with higher cutoff frequencies necessarily follows. Current RC filters generally achieve higher cutoff frequencies by increasing the resistance and decreasing the capacitance. Increasing the resistance has the negative impact of increasing the insertion loss in the pass band so the usual method is that of lowering the capacitance. However, the most severe limitation of these implementations is the limited frequency response roll off rate. While the cutoff frequency can be adjusted upwards to accommodate the higher data rates, the rejection band remains fixed and consequently, a relatively slow roll off rate results and the filter attenuation at radio frequencies is compromised.